This invention relates generally to water purification systems of the reverse osmosis type for producing a supply of relatively purified water for drinking, cooking, etc. More particularly, this invention relates to an improved pressure relief valve for use in such water purification systems, wherein the pressure relief valve is designed for accurate and reliable operation to prevent the pressure of produced purified water from exceeding a predetermined pressure limit.
Reverse osmosis water purification systems in general are relatively well known in the art for producing a supply of purified water from an incoming supply of ordinary feed or tap water or the like. In such systems, the feed or tap water is coupled to a reverse osmosis module including an appropriate membrane for separating the feed water supply into a relatively pure water supply and a relatively impure or reject water supply. The purified water supply is normally coupled for flow into a suitable pressurized storage reservoir to await dispensing through a conventional faucet valve or the like. Conversely, the reject water supply is coupled for flow to and discharge as waste through a suitable drain path. As is known in the art, for proper operation of the reverse osmosis module, the reject water drain path includes a restrictor which functions to maintain a substantial backpressure acting upon the membrane.
In many water purification systems of the general type described above, the storage reservoir comprises a compact tank or vessel having an internal flexible bladder which separates the tank interior into two distinct chambers. The produced purified water is coupled for flow into one of these chambers, whereas the other chamber contains a compressible gas such as air. As the tank fills with produced purified water, the compressible gas is reduced in volume to progressively increase the pressure acting through the bladder upon the purified water for dispensing purposes. However, this increasing pressure applied to the purified water reduces the pressure differential across the reverse osmosis membrane to correspondingly reduce the operational efficiency of the reverse osmosis module. That is, as the pressure of the purified water approaches the pressure of the reject water supply upstream of the restrictor, the operational efficiency of the reverse osmosis module progressively diminishes. If the purified water pressure is allowed to reach equilibrium with the reject water pressure, the desired pressure differential across the membrane is eliminated to result in potential migration of impurities through the membrane to the produced purified water.
In the past, pressure relief valves have been proposed to prevent pressurization of the produced purified water beyond a selected pressure limit relative to the pressure of the reject water supply. That is, such pressure relief valves are designed to maintain a minimum pressure differential across the reverse osmosis membrane during all conditions of system operation, including a substantially filled condition for the purified water reservoir. Such relief valves function by the use of complex valve structures designed to bleed produced purified water into the reject water supply when the predetermined pressure limit is reached. See, for example, U.S. Pat. Nos. 3,542,199; 3,568,843; and 4,077,883. However, such prior pressure relief valves have not provided reliably accurate pressure control of a purified water supply. Moreover, such prior relief valves have utilized valve structures and related seal components which undesirably leak pressurized reject water into the produced purified water supply during certain failure mode conditions.
There exists, therefore, a significant need for an improved pressure relief valve for use in reverse osmosis water purification systems, wherein the improved pressure relief valve is designed for accurate pressure limiting operation with respect to produced purified water, without permitting inadvertent leakage of reject water into the produced purified water supply. The present invention fulfills these needs and provides further related advantages.